Power cable to workshop/garage

[ban-all-sheds]

You're quibbling again. 20A is "62.5% of the In of the 32A OPD". I agree that the regs to do not say anything about allowing a ring final when the CCC of the cable is 62.5% of the In of an OPD with any In other than 32A - but I didn't say or suggest that they did.

Is is not quibbling.

The regulations specify a minimum Iz of 20A, not 62.5% of 32A.

That was precisely what I was suggesting. BS7671 clearly does not allow such a design - so, as you say, any designer who wanted to use it would have to be able to argue that it was at least as safe as what BS7671 does allow.

Good luck finding one, or finding an LABC prepared to accept a non-electrician's assertion on an EIC that what he'd done was OK.

However, if, as above, a designer can successfully argue that his/her design is at least as safe as a design which the regs allow, then I don't see that the speculated 'intent' (whatever it was) of those who wrote the current regs would be of any relevance, would it?

No, if the designer decided that JPEL/64 had no reason whatsoever for the change, that it was entirely whimsical, then it would be of no relevance to him.

As I said before, if we are going to speculate about intent/reasons, I would suspect that they were not very confident that CCC always properly took into account installation methods and de-rating factors throughout the length of the cable run, and therefore were being fairly cautious by writing the reg in terms a cable of minimum CSA 2.5mm² which was allowed to have a CCC as low as 20A .

Such caution could have been enshrined in a factor of 0/625 instead of 0.67. But they made an entirely reason-free decision not to.

The one argument I was expecting some people to present, but which hasn't yet been wheeled out, is that accessories to BS1363 may not be 'rated' for use in a circuit >32A. I'm not sure about the specification.

In your proposed circuit no accessory would "see" more than 27A.

 

[jmac80]

Hi Guys
So had a sparky round, He's happy for me to put a 10mm cable from CU in house to garage. He will wire it in once in place.
He said i could go 6mm but may as well just put 10mm as it doesn't cost much more for this short run and would give more options in the future (you never know)

When he started getting into it all it was way over my head and i just agreed and nodded

Think he said a 40a mcb from non rcd side to feed the garage CU.
I got lost at this bit..
How big will the garage Cu likely be?
I imagine 1 ring for sockets, 1 for lights, then does each 16a socket need there own mcb?

 

[EFLImpudence]

How big will the garage Cu likely be?

Not very.

I imagine 1 ring for sockets, 1 for lights,

Not necessary to have a ring for the sockets.

then does each 16a socket need there own mcb?

Yes, but you really only have capacity for using two at 16A at any one time.
If you only intend to use one at a time then they could all be on the one mcb.